The present invention relates to cleaning apparatuses of the type used for cleaning soot, slag, ash and other accumulated deposits from heat exchange surfaces to maintain efficiency in their operation. More specifically, the present invention includes a nozzle structure which is particularly applicable, but not necessarily limited, to sootblower cleaning devices such as those types used in cleaning large scale boilers.
Generally, sootblowers include a lance tube which is connected to a pressurized source of blowing medium. In a retractable sootblower, the lance tube is advanced into and retracted from the interior of the boiler as the blowing medium is discharged in a stream or jet from nozzles on the end of the lance tube. In a stationary sootblower, also known as a wallblower, the lance tube is fixed in position within the boiler and the blowing medium is discharged from nozzles positioned therealong. In either type, the impact of the discharged blowing medium with the deposits accumulated on the heat exchange surfaces produces both a thermal and mechanical shock which dislodges the deposits U.S. Patents which generally disclose sootblowers include the following, which are hereby incorporated by reference U.S. Pat. Nos. 3,439,376; 3,585,673; 3,782,336; and 4,422,882.
A continuing problem associated with cleaning in this fashion is the tendency of the discharged jet of blowing medium to lose its coherency and integrity between the time it is discharged and the time it is impinged upon the surface being cleaned. Various factors contribute to the loss of coherency, including the disturbance of the jet by convection currents within the boiler and the existence of turbulent blowing medium flow patterns in the nozzle structure itself. These and other disturbances produce a fanning out of the jet reducing the average and maximum jet velocity, and also lowering the peak impact force at impingement. As a result, the effectiveness and efficiency of the cleaning operation per mass of fluid discharged is reduced. While the coherency problem is encountered at short cleaning distances, e.g. 12 inches, it is particularly pronounced at the extreme cleaning distances common in high capacity pressure boilers, e.g. 36 inches and beyond. The foregoing problem is aggravated by the limitations on nozzle design and nozzle inlet conditions due to the restricted mounting space available within the lance tube.
Conventional sootblower nozzles are positioned perpendicular to the flow of blowing medium within the sootblower lance tube and define a straight nozzle passageway directing the fluid discharge in a radial direction. Therefore, the length of the nozzle is limited to less than inside diameter of the lance tube. Since stream coherence generally improves with increases in the ratio of the nozzle length to its diameter, termed the L/D ratio, conventional nozzles have limited coherence potential.
An additional problem generally associated with the nozzle design and particularly associated with lance tube design is that the distal end of the lance tube, that end being inserted into the boiler, is subjected to extreme temperatures. The resulting damage often requires replacement of the lance tube at a considerable expense.
With the above considerations in mind, it is an object of the present invention to provide an improved nozzle structure having enhanced cleaning efficiency and effectiveness.
A related object of the invention is therefore an increase in the cleaning effectiveness per mass of fluid discharged from the lance tube.
Another object of the invention is the prevention of thermal damage to the distal end of the lance tube.
The objects, benefits and advantages of the present invention are achieved by providing the lance tube with an improved nozzle structure. The nozzle structure is adapted to be supported in the wall of the lance tube and comprises a conduit or tubular element having a bore extending substantially centrally therethrough to define an inlet opening and a discharge opening. The inlet opening is in communication with the interior of the lance tube while the discharge opening is disposed for discharging the fluid blowing medium in a directionally oriented jet.
The conduit of the nozzle exhibits a length which is substantially greater than the diameter of the bore extending therethrough. Thus, the nozzle structure exhibits a high length to diameter (L/D) ratio. The conduit is also of an orientation which aligns that portion defining the inlet opening, hereinafter the inlet throat, substantially axially with the lance tube. A further feature of the present nozzle structure is that the inlet opening of the conduit is preferably oriented in a direction facing the distal end of the lance tube.
Positioned within and adjacent to the distal end of the lance tube is a means for reversing the flow direction of the fluid blowing medium therein. This reversal or redirection serves several purposes. One is that it directs the flow of fluid blowing medium into the inlet opening and throat of the conduit. Also, since the redirecting means is in surface-to-surface contact with the distal end of the lance tube, heat is transferred from the distal end of the lance tube to the fluid blowing medium thereby cooling the tip or end of the lance tube.
Two embodiments of the present invention are being disclosed. In either embodiment, the flow of fluid blowing medium is reversed at the distal end of the lance tube, cooling the end of the tube, and directed generally axially into the inlet throat of the conduit. By directing the flow of fluid blowing medium axially into the conduit, the characteristics of the flow pattern are improved to a more laminar state by the high L/D ratio of the conduit. This results in better jet coherency at greater distances from the discharge opening and also results in an increased cleaning efficiency per mass of fluid discharged. At discharge, the fluid blowing medium has been shaped into a tight, high velocity jet which is resistant to the cross current influences of convection gases present in the boiler.
Additional benefits and advantages of the present invention will become apparent to those skilled in the art to which this invention relates from the subsequent description of the preferred embodiments and the apparent claims, taken in conjunction with the accompanying drawings.